Short inverted repeat sequences have been observed in the DNA flanking the 5' and 3' termini of a pair of coordinately expressed chorion structural genes of the silkmoth Bombyx mori. When superhelical cloned DNA containing the two chorion genes is digested with S1 nuclease, several sites are specifically cleaved including those around the centers of the putative cruciform structures resulting from the short inverted repeat sequences. The possible implication of conformational changes in the DNA surrounding the chorion structural genes in the process of determination of the developmental specificity and the coordinate transcriptional regulation of these genes is discussed.